The present invention relates to a video display apparatus for fetching and displaying a video signal, or more in particular to a video display apparatus capable of fetching a plurality of video signals having different scanning frequencies (horizontal scanning frequencies and vertical scanning frequencies) and displaying on the same screen by synthesis or switching, and a screen display system using the same video display system.
In conventional video display apparatuses, which typically include common television receivers and computer display units, in the case where an attempt is made to display a plurality of types of video signals on the same screen by synthesis or switching, the video signals intended for display are limited to those having the same scanning frequency (horizontal scanning frequency and the vertical scanning frequency) or to the use with the display unit adapted for multi-scanning.
These techniques are disclosed, for example, in JP-A-61-127285, JP-A-61-128691, JP-A-62-208766, JP-A-63-142783, and JP-A-4-342295. A multi-screen display system, on the other hand, is disclosed in JP-B-50-32009 and JP-A-4-280291.
There is a demand, however, for displaying video signals of different scanning frequencies by synthesis or switching on the same screen. The Hi-Vision video signal and the video signal for the personal computer, for example, has a scanning frequency different from that of the video signal according to the standard NTSC system. It is therefore needless to cite specific examples to consider it convenient if a static image such as statistical data prepared on a personal computer can be displayed by synthesis or switching on a dynamic image of the video signal based on the NTSC system.